1. Field
The present disclosure relates generally to coating metal pipes, and more particularly to applying a uniform coating to the interior of relatively long tubular structures.
2. Description of the Related Art
Electroless Nickel Coating (“ENC”) is a nickel plating process for chemically applying nickel alloy deposits onto metallic substrates using an autocatalytic immersion process without the use of electrical current. ENC is often applied to relatively short tubular components (e.g., 10-foot lengths), by dipping individual lengths of pipe vertically into a sump tank or bath with vertically spaced spargers to inject solution into the long body of the pipe. This conventional coating technology suffers a number of limitations including the depth of the sump bath and correspondingly the height of the ceiling of the workspace into which the treated body must be positioned. Similarly, it is difficult and time consuming, thus inefficient, to secure the tubular substrates in position vertically while changing them and replenishing the solution between batches. A further disadvantage of the conventional vertical dipping process for coating long tubular structures is the limited ability to control the distribution of the nickel solute so as to permit it to plate long curved surfaces uniformly. In many applications it is important that the nickel coating be uniform. Further, for applications in oil-producing regions, it is often necessary to use much longer tubular goods (e.g., 40-foot lengths). Accordingly, it is desirable to find a way to consistently apply uniform electroless nickel coatings over very long curved surfaces.
Typically, ENC is only applied to shorter lengths of pup joints, because existing processes fail to efficiently coat full length tubular joints with consistent results. The prior art in the ENC industry has concentrated on teaching variations on vertically oriented bath tanks and pipes, which disadvantageously requires deep tanks and a tall building to plate long pipes. See, e.g., U.S. Pat. No. 4,262,044 and U.S. Pat. No. 6,245,389.